Welding is a common way to join similar and dissimilar materials in a wide range of industries, including consumer electronics, home products and appliances, farming, construction equipment, transportation systems, and the like.
The dissimilar materials can include a dissimilar metals, dissimilar polymers, or combinations of polymers and metals. The manufacturer can select favorable characteristics, such as being lightweight, highly-conformable or shapeable, strong, durable, or having a desired texture or color by combining some polymer or composite materials with other materials. An article of manufacture may include various components (exterior, interior, or decorative features) where materials are selected and configured to withstand a hot and/or chemically aggressive environment or for painting or chemical resistance over time.
Processes for joining similar or dissimilar materials include mechanical joining (e.g., bolts and rivets), fusion joining (e.g., fusion arc welding and laser welding), solid-state joining (e.g., friction-stir welding and ultrasonic welding), brazing or soldering, and adhesive bonding, among others.
Joining materials robustly and without great expense is a challenge. Considerations include chemical, mechanical, and thermal behaviors of materials being joined. Adhesive bonding presents many benefits including being relatively cost effective and non-intrusive.
Conventional adhesive-bonding techniques involve applying adhesive between two usually smooth surfaces. Turning to the figures, and more particularly to the first figure, FIG. 1 illustrates a conventional adhesive-bonded system 100. The system 100 includes a first workpiece 110 joined to a second workpiece 120 by an adhesive 130.
In some cases, a surface is polished or scored on a micro-scale, such as to remove surface contamination and/or add roughness.
Conventional techniques have shortcomings. While conventional adhesively bonded joints have relatively strong shear strength, keeping the respective workpieces from moving laterally (or parallel) with respect to each other, they tend to have relatively weak peel strengths. Example shear forces are indicated by arrows 101 in FIG. 1.
Adhesive does not generally do well alone at countering non-lateral forces, such as peel or pull forces. Example peel forces are indicated by arrows 103 in FIG. 1. Peel forces tend to pull the workpieces away from each other. In operation, cracks form in the adhesive of the joint and propagate through the adhesive, such as generally laterally, without obstacle, weakening the joint 100.
With further reference to the figures, FIG. 6 shows the fracture surfaces of an example joint 610. The joint 610 corresponds to a conventional system like the system 100 of FIG. 1. Lines shown in the joint 610 represent cracks that have propagated through the adhesive in response to peel force input.
Designers have tried to solve the aforementioned shortcomings by adding mechanical fasteners such as rivets. This is accompanied by ancillary shortcomings, though, such as added cost, product weight, and potential for later galvanic corrosion.
While adhesive bonds can be strong, depending mostly on the adhesive used, stronger adhesive-based bonds are desired and now possible.